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108 Power flows in compensation and control studies

Fig. 4.1 SVC. (a) structure formed by fixed capacitor and TCR; and (b) variable susceptance representation.

speed of response. It is used extensively to provide fast reactive power and voltage
regulation support. It is also known to increase system stability margin and to damp
power system oscillations (Kundur, 1994).
In power flow studies the SVC is normally modelled as a synchronous generator
with zero active power generation; upper and lower limits are given for reactive
power generation. The generator representation of the SVC is changed to a constant
admittance if the SVC reaches one of its limits (IEEE Special Stability Controls
Working Group, 1995).
A more flexible and realistic SVC power flow model is presented in this chapter. It
is based on the concept of a non-linear shunt reactance, which is adjusted using
Newton's algorithm to satisfy a specified voltage magnitude at the terminal of the
SVC (Ambriz-Perez et al., 2000). The schematic representation of the SVC and its
equivalent circuit are shown in Figure 4.1, where a TCR is connected in parallel with
a fixed bank of capacitors. A more detailed schematic representation of the TCR is
shown in Figure 1.9.
An ideal variable shunt compensator is assumed to contain no resistive compon-
ents, i.e. G SVC ˆ 0. Accordingly, it draws no active power from the network. On the
other hand, its reactive power is a function of nodal voltage magnitude at the
connection point, say node l, and the SVC equivalent susceptance, B SVC
P l ˆ 0
(4:1)
2
Q l ˆ jV l j B SVC

4.2.2 The TCSC

The TCSC varies the electrical length of the compensated transmission line with little
delay. Owing to this characteristic, it may be used to provide fast active power flow
regulation. It also increases the stability margin of the system and has proved very
effective in damping SSR and power oscillations (Larsen et al., 1992).